The use of gas bubbles for mixing the contents of a tank or other container is well known. For instance, blending lubricating oils with additives is done in a large tank in which compressed air is released into the tank at the bottom through a mechanical device called a "spider". It is an apparatus made of crossed pipes with holes in them which allows small bubbles to leave the pipe at the bottom of the tank and rise to the top. Spiders do cause a blending of the material or product in the tank but the blending action is slow and not always complete throughout the container or tank.
Other means for mixing or blending would be mechanical mixtures such as paddles, beaters and, of course, pumping. Mechanical mixers and pumps require routine maintenance and those mechanical mixers which are available may require additional external tank reinforcement to support the drive mechanism as well as the internal components which provide agitation. The air spiders for the most part are maintenance free and have minumum in-tank hardware but are not particularly efficient. The blending time required can vary from a few hours to several days depending on the nature of the liquids being blended. A continuous stream of air produces small bubbles and results in large amounts of entrained air. It will be appreciated that a constant flow of air through an air spider also results in a high consumption of compressed air and thus energy. Mechanical blenders or mixers are also recognized for their high energy requirements.
The only pertinent references known are U.S. Pat. Nos. 3,179,379; 4,136,970; and 4,168,913. The patents cited show either continuous or intermittent air injection at the bottom of a tank. None of the references, however, shows details of the claimed combination of structural elements and method steps as set forth in the instant invention.
Cabrera, U.S. Pat. No. 4,136,970 does not concern itself with regulated air pressure, with spherical shape of the bubbles, or with injecting bubbles in the timing sequence of the instant invention.
Italian Patent No. 545,047 to Klinger is likewise not pertinent since it is concerned only with blending and mixing dry particulates such as cement and lime. Neither in structure nor in operating principal is it pertinent to the invention of this application.